Hair extensions will stop itching when their scalp has returned to its usual state. As we know, people with sensitive scalp may naturally take slightly longer than someone with a less sensitive scalp to adjust to a new set of hair extensions. An average set of hair extensions weighs approx. 100g. Hair extensions will add weight to your scalp. Thus, the first few days, your scalp may go into overdrive trying to cope with the sudden change in normality. However, this is a very common side effect of this is for your scalp to itch. And, this should only be mild and last a few days whilst your scalp gets used to the change.